Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$30.82	4.688%	$32.2648	$32.26	$32.25	$32.30
Purchase #2	$179.67	3.436%	$185.8435	$185.84	$185.85	$185.80
Purchase #3	$71.60	3.834%	$74.3451	$74.35	$74.35	$74.30
Purchase #4	$55.68	12.456%	$62.6155	$62.62	$62.60	$62.60
Purchase #5	$92.82	11.354%	$103.3588	$103.36	$103.35	$103.40
Purchase #6	$195.88	13.261%	$221.8556	$221.86	$221.85	$221.90
Purchase #7	$106.26	3.415%	$109.8888	$109.89	$109.90	$109.90
7 purchase totals =	$732.73		$790.1721	$790.18	$790.15	$790.20